SELECTED QUARTERLY CONSOLIDATED FINANCIAL DATA - Selected quarterly consolidated financial data (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Selected quarterly consolidated financial data	Sep. 30, 2013 Selected quarterly consolidated financial data	Jun. 30, 2013 Selected quarterly consolidated financial data	Mar. 31, 2013 Selected quarterly consolidated financial data	Dec. 31, 2012 Selected quarterly consolidated financial data	Sep. 30, 2012 Selected quarterly consolidated financial data	Jun. 30, 2012 Selected quarterly consolidated financial data	Mar. 31, 2012 Selected quarterly consolidated financial data
Statement of Income
Interest and dividend income				$ 5,479	$ 5,431	$ 5,434	$ 5,406	$ 5,426	$ 5,607	$ 5,766	$ 5,858
Interest expense				686	772	801	803	992	1,035	1,080	1,175
Net interest and dividend income				4,793	4,659	4,633	4,603	4,434	4,572	4,686	4,683
Provision for loan losses				190	240	240	396	380	330	180	180
Trust and Wealth Advisory				775	750	824	725	772	683	735	755
Service charges and fees				612	595	575	516	561	559	547	521
Gains on sales of mortgage loans, net				78	69	153	279	394	568	263	372
Mortgage servicing, net				38	(37)	8	26	76	(9)	(5)	(84)
Securities gains										267	12
Other				68	82	90	79	74	86	83	83
Non-interest income				1,571	1,459	1,650	1,625	1,877	1,887	1,890	1,659
Non-interest expense				4,977	4,643	4,610	4,705	5,334	4,693	5,026	4,500
Income before income taxes				1,197	1,235	1,433	1,127	597	1,436	1,370	1,662
Income tax provision				214	219	289	187	26	296	254	412
Net income	4,083	4,077	4,112	983	1,016	1,144	940	571	1,140	1,116	1,250
Net income available to common shareholders				943	976	1,103	900	531	1,094	1,069	1,167
Financial Condition
Total assets				587,109	589,481	600,712	597,343	600,813	611,037	600,857	598,950
Loans, net				438,178	420,306	416,729	406,258	388,758	377,377	377,212	371,709
Allowance for loan losses				4,683	4,656	4,632	4,686	4,360	4,179	4,208	4,166
Securities				99,831	105,156	111,950	124,004	132,034	131,412	141,409	151,666
Deposits				477,369	479,869	492,040	487,773	491,215	490,206	477,910	472,686
Repurchase agreements				2,554	3,870	2,980	2,329	1,784	2,941	6,181	10,359
FHLBB advances				30,411	30,801	31,187	31,574	31,980	42,392	42,801	43,207
Shareholders' equity				72,790	71,211	71,489	72,206	71,997	70,374	69,126	68,067
Non-performing assets				$ 7,549	$ 9,737	$ 9,639	$ 9,297	$ 10,104	$ 9,870	$ 8,409	$ 7,606
Per Common Share Data
Earnings, diluted and basic				$ 0.55	$ 0.57	$ 0.65	$ 0.53	$ 0.31	$ 0.65	$ 0.63	$ 0.69
Cash dividends declared				$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28
Cash dividends paid				$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28
Book value				$ 33.21	$ 32.28	$ 32.45	$ 32.88	$ 33.14	$ 32.18	$ 31.44	$ 30.83
Market price: (a) High				$ 28.00	$ 29.95	$ 28.00	$ 26.44	$ 28.41	$ 26.39	$ 26.49	$ 26.95
Market price: (a) Low				$ 25.50	$ 25.52	$ 25.18	$ 23.55	$ 23.16	$ 23.11	$ 23.25	$ 22.51
Statistical Data
Net interest margin (fully tax equivalent)				3.71%	3.51%	3.54%	3.54%	3.32%	3.39%	3.58%	3.54%
Efficiency ratio (fully tax equivalent)				71.77%	71.72%	68.88%	70.93%	71.45%	66.05%	66.39%	66.86%
Return on average assets				0.64%	0.64%	0.74%	0.61%	0.35%	0.71%	0.72%	0.78%
Return on average shareholders' equity				6.69%	7.05%	7.81%	6.45%	3.85%	8.05%	8.10%	9.05%
Weighted average equivalent shares outstanding, diluted				1,691	1,691	1,691	1,690	1,690	1,690	1,689	1,689